The present invention relates generally to gas generant compositions, especially liquid gas generant compositions employed in the inflation of passive vehicle occupant restraint systems.
Various inflators for inflating passive vehicle occupant restraint systems (known colloquially in the art as xe2x80x9cair bagsxe2x80x9d) are known. Among the various types of inflators is one that utilizes a quantity of stored compressed gas which is selectively released to inflate the air bag. A related type of inflator generates a gas source from a solid combustible gas-generating material which, upon ignition, provides a quantity of gas sufficient to inflate the air bag. In still another type (known as a hybrid inflator), the air bag inflating gas is provided by the combination of a stored compressed gas and the combustion products of the gas generating material.
Inflators which depend entirely or partially on the generation of gases by virtue of combustion of solid combustible materials have several disadvantages. For example, the burning of the propellant and the initiation materials in such inflators results in the production of undesired particulate matter. Thus, using inflators that are particulate-containing or which generate particulates upon combustion as part of a passive restraint system in a vehicle might result in undesirable particulates being released into the occupant zone of the vehicles and thereby inhaled by the occupants.
One prior inflator is disclosed in commonly owned U.S. Pat. No. 5,589,141 to Sides et al (the entire content of which is expressly incorporated hereinto by reference). In the Sides et al ""141 patent, the composition of the inflator comprises conducting ignition in the presence of an ammonium nitrate oxidizer and using a suitable propellant, e.g., aminoguanidine nitrate or a nitramine, such as hexahydro-1,3,5-trinitro-s-triazine (RDX) and/or octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazine (HMX), and in the presence of argon and a molecular oxygen-containing gas. The ratio of the oxygen-containing gas to argon is variably selected so as to provide only non-toxic reaction products in the exhaust gas.
There is still a desire to develop particulate-free propellants for air bags. It is towards fulfilling that desire that the present invention is directed.
Broadly, the present invention is embodied in liquid monopropellants for passive vehicle restraint systems (e.g., air bags) comprised of an aqueous solution of a water-soluble oxidizer and an alcohol fuel miscible with the oxidizer. Most preferably, the oxidizer is ammonium nitrate or hydrogen peroxide, while the alcohol fuel is a lower alcohol such as methanol, ethanol or propanol.
The liquid monopropellants of this invention will advantageously have an oxidation ratio (OR) of greater than about 0.95, and more preferably greater than about 1.00 thereby yielding suppressed amount of carbon monoxide and hydrogen combustion gases. As a result, the combustion products of the liquid monopropellants of this invention will be essentially non-toxic and non-flammable. Furthermore, combustion of the monopropellants in accordance with this invention will be particulate-free.
These and other aspects and advantages will become more clear from the following detailed description of the preferred exemplary embodiments thereof.
The gas generant solutions of this invention are liquid monopropellants. As used herein and in the accompanying claims, the term xe2x80x9cmonopropellantxe2x80x9d and like terms is meant to refer to a liquid mixture in which the oxidizer and fuel are dissolved in one another to form a miscible liquid solution thereof. The liquid monopropellants of this invention, moreover, are aqueousxe2x80x94that is, contain a significant amount of water. Most preferably, the liquid monopropellants will contain at least about 20 wt. % of water, and more preferably between about 20 wt. % to about 35 wt. % water. All weight percentages expressed herein are based on the total weight of the liquid monopropellant.
The liquid monopropellants will necessarily comprise a water-soluble oxidizer. Most preferably, the oxidizer is ammonium nitrate (AN), hydrogen peroxide (H2O2) or nitric acid (HNO3). The oxidizer will be present in an amount of at least about 50 wt. %, and more preferably between about 60 wt. % to about 75 wt. %.
The fuel employed in the liquid monopropellants of this invention is a water-soluble organic compound that is miscible with the oxidizer. Most preferably, the fuel is a lower alcohol, such as methanol, ethanol, propanol (e.g., isopropanol), butanol, pentane diol, allyl alcohol, glycerol and the like. The alcohol fuel will be present in an amount between about 5 wt. % to about 15 wt. %.
Other organic fuels that are soluble in water and/or alcohols that may be employed in the practice of this invention include guanidine, guanidine nitrate, guanidine carbonate, guanidine acetate, cyanoguanidine, aminoguanidine nitrate (and other aminoguanidine analogs of the guanidine compounds) glycine and its water/alcohol soluble derivatives, water-soluble organic acids, amines, amides, ethers, esters, nitriles and the like. In addition water-dispersible compounds such as surfactants (alkylphenyl hydroxy terminated polyethers), gums such as guar gum xanan gum, cellulosics, starches and the like, may be used if desired. These fuels may be used singly or in combinations of two or more or the same.
The three necessary componentsxe2x80x94that is, oxidizer, fuel and waterxe2x80x94will be present in an amount sufficient to yield an oxidation ratio (OR) which is greater than about 0.90. For example, in nitrogen-containing propellants, the oxidation ratio should be between about 0.90 to about 1.0. IN propellants that do not contain nitrogen, the oxidation ratio should be greater than about 1.0.
The present invention will be further understood from the following non-limiting Examples.